1. Field of the Invention
The present invention relates to a hypermedia system used in a network environment, and more particularly to a hypermedia system for managing node link information intensively by use of a directory server provided in a network.
2. Description of the Prior Art
In recent years, a system called a hypermedia system has attracted considerable attention as a management technique of information in computers. The hypermedia system directly associates data files whose contents are related each other to process multi-media data including image data and voice data as well as text data based on a hypertext structure in which data is retrievable interactively without being aware of file names. Hereinafter, a data file treated here is referred to as a node.
As a hypermedia system in a network environment, for example, the World-Wide Web as disclosed in a paper entitled, "The World-Wide Web" published in the Communication of the ACM, Vol. 37, No. 8, pp. 76-82, issued August 1994 is prevailing. FIG. 8 illustrates a construction of this type of conventional hypermedia system.
As shown in the figure, a conventional hypermedia system includes a client computer 81 (hereinafter, simply, referred to as a client) and server computers 82a to 82c (hereinafter, simply, referred to as a server) connected via a network 80. The client 81 and the servers 82 store a plurality of contents files for storing contents of nodes such as a hypertext. The location of each contents file is specified by a node identifier (in the above-mentioned World-Wide Web, a node identifier called a URL (uniform resource locator) is used). In FIG. 8, each arrow indicated by a solid line indicates a data flow and each arrow indicated by a dashed line indicates the connection relationship between two nodes.
The client 81 accesses one of the servers 82a to 82c in the network 80 on the basis of a node identifier specified by a user and obtains a contents file of a node indicated by the node identifier to output the contents. For example, if the node identifier of a contents file 801 of the server 82a is specified in FIG. 8, the client 81 achieves the contents file 801 from the server 82a and displays its contents (such as texts) on a display screen. The displayed contents file 801 includes a definition of an anchor area 811, whose designation specifies the node identifier of a contents file 802 associated with this area. Then, the client 81 accesses the server 82b in the network 80 and obtains the contents file 802 to output its contents.
Additionally, the Japanese Patent Disclosure (Kokai) No. 7-44447 discloses a construction in which a hypertext apparatus existing in a host in a network inquires the location of a contents file from a directory server and then accesses the desired contents file, by use of the directory server provided for managing the titles and locations of contents files in the network so as to intensively manage the contents files scattered in the network.
The hypermedia system shown in FIG. 8, however, cannot know information about the contents of a contents file nor link data contained in a node specified by the client until it reads the contents file of the node. In addition, also as described in the Japanese Patent Disclosure (Kokai) No. 7-44447, the directory server manages the locations of contents files only, but cannot know the contents of the contents files nor the connection relationship between nodes.
To proceed with navigation efficiently, it is necessary to easily grasp the entire hypermedia structure composed of node data scattered in the network and link data indicating the connection relationship between nodes and also information about the contents of respective nodes to some extent. In the above conventional techniques, however, it is required to read nodes one by one to follow links, in order to grasp the contents of the nodes, and therefore, it has the disadvantage of requiring a large number of operation times and an enormously-long processing time.
Therefore, a first object of the present invention is to provide a hypermedia system which improves the efficiency of users' navigation works in a network environment.
Further, if a directory server is prepared for managing node link information intensively, it is required to update directory information of the directory server whenever node data or link data is updated on each server, which puts an increased burden on a server manager.
Therefore, a second object of the present invention is to provide a hypermedia system having a means for updating directory information on a directory server efficiently.
Still further, if directory information is updated with each server regularly checked by a directory server, there is a concentration of checks on node data and link data and of the extraction processing of the directory information, which puts an increased load on a host in which the directory server is working if there are a larger number of servers or link data of nodes on the servers.
Therefore, a third object of the present invention is to provide a hypermedia system which reduces a load in data updating in servers.